FWIW I have a medium Ice cap pro that I added on a 300g system. It pulled my nitrates down from 15-20 to 3-5, and has phosphate running much lower ranging from .03-.1. I run lights 16 hours per day. I scrape it every 3 weeks. Here’s my last harvest
I like to dose kalk precisely to keep levels stable. In an ato your daily evaporation changes, so you kalk dosage would change. I prefer an ecotech versa and an avast kalk stirrer to dose the same amount daily.
Can’t tell from your pics but algae and sand in the seams is how it starts. Consider yourself lucky to have noticed it. I would prepare to break it down asap given Red Sea tank reputations.